1. Field of the Invention
The subject invention has wide application and may be used to advantage in any fluid control apparatus. It has particular utility where extremely high hydraulic pressures are used such as is the case in airless spraying systems where high fluid pressures and impinging fluid streams atomize the fluid in lieu of air. The use of the subject invention is particularly advantageous in can production facilities for spray painting and lacquering the insides of cans, where the spraying device must be able to instantaneously start and stop the spray as the individual cans pass through the spraying station necessitating extremely quick valve response capability.
2. Prior Art
The can making industry for years has been geared to air spray systems in which air is used to atomize the fluid. Many problems are associated with air systems and any such system necessarily must be dependent upon the available air supply. Compressed air supplies are affected by many factors such as temperature and humidity; and the pressure in plant supply lines can be easily caused to vary by these factors which will adversely affect the operation.
Many problems of air atomized spray methods may be eliminated by the use of an airless spray method, however, much higher fluid pressures then were necessary in the air systems are necessary to properly atomize the fluid. Standard solenoid valves where springs bear against armature and pilot which make it necessary that spring pressure as well as the high fluid pressure be overcome simultaneously upon coil energization have proven to be inadequate for spraying cans with coating materials. For use in the assembly line production of cans, it is desirable to have a response time for the valve to open upon coil energization on the order of 4 milliseconds. The standard solenoid valves as described cannot produce this quick reaction time to make such an airless system feasible.
The design of a quick response time valve for airless fluid atomizing systems is governed by a number of considerations which have not been developed in the past primarily because quick reaction spraying systems have been air atomization systems not involving the high fluid pressures which are necessary for airless systems. Valve mechanisms of the type disclosed by T. C. Knaebel et al in U.S. Pat. No. 2,965,350 which issued on Dec. 20, 1960 do not provide fast response times as needed for some application such as production line can spraying. The knaebel et al patent discloses a hermetically sealed valve mechanism that provides for a high flow rate by a double valve system in which a pilot valve 26 is opened by means of armature 30 as controlled by the energizing of magnetic coil 42, all of this which then allows main valve 16 to be opened by fluid pressure alone to provide the desired high rate of flow while sacrificing response time.
U.S. Pat. No. 3,473,780 which issued on Oct. 21, 1969 to G. E. Harms discloses a solenoid reaction jet actuator which opens for a time duration as controlled by the mechanical characteristics of the valve and is independent of the driver electronics. Such a design was deemed necessary for the use of jet actuators in spacecraft to eliminate weight and reliability problems of valves controlled by characteristics of the drive circuitry. The valve of the Harms patent while desirable in its limited application and related uses, lacks utility where it is necessary that the valve duration be adjustable and therefore dependent on the drive circuitry.